1. Technical Field
The present disclosure relates to thermal control in memory systems and, in particular, to determining and communicating operating temperatures of solid state memory devices.
2. Related Art
The temperature of a semiconductor memory, such as a RAM (random access memory) is largely determined by its activity level (rate of reads and writes into the memory cells) and its environment. If the temperature becomes too high, then the data stored in the memory may be corrupted or lost.
In addition, as the temperature of a solid state memory increases, the memory loses charge at a faster rate. If the memory loses charge, then it loses the data that was stored in its memory cells. RAM chips have self-refresh circuitry that restores the lost charge at periodic intervals. As the temperature increases the self-refresh rate must be increased in order to avoid losing the data. This increases power consumption.
In order to keep the refresh rates low and to avoid damage to the memory or loss of data, some information about the memory temperature must be known. The more accurate the temperature information, the hotter the memory may be permitted to run and the lower the refresh rate may be without risk of data loss. If the temperature information is not reliable or accurate, then the memory is run at a slower access rate and a faster refresh rate then necessary in order to provide some margin for error. Accurate temperature information may also be used to control cooling fans and other thermal controls.
Memory is often packaged in modules that contain several similar or identical IC (Integrated Circuit) chips, such as DRAM (Dynamic Random Access Memory) chips. The temperature of each chip may be different, depending on its level of use, available cooling and its own unique characteristics. Other devices on the memory module may have different temperatures as well. In order to accurately monitor all aspects of such a memory module, expensive thermal circuitry is required for each DRAM chip and maybe even for different portions of each DRAM chip. In addition, a communication system is required to transfer all of the temperature information to a device that can interpret the information and cause some action to be taken, if necessary. This additional circuitry may significantly increase the cost of the memory module.